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Yes, thats thrue, but when i put resistor between BD139 emmiter and two output transistor bases this mean that if no zero voltage on power resistor (beacause of some unfourable reasons) current flows through output transitor in any case also without battery because there is forward biased.

I hope that i am right.

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Have you any idea how to avoid this effect?

It could be ideal that no current flow through output transistor when battery is not connected onto circuit and 0V is on discharge power resistor via OP feedback.

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Thanks!

I tried this and works fine, i put the 680E resistor between emmiter and bases, but there is one think, it can't possible to make no current flow throught circuit if battery disconnected, some current always flow into transistors, around 1.5ma regarding my simulation.

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Transistor is burned out again so i just wondering that the main problem is that at power supply present and before output of MCU provide zero voltage to + input of OP very high current through BD139 and in bases of output transistor because battery not connected at start.

As is said i have no problem with circuit where i use PNP uput transistors because at start no current was flow through circuit because no base current flow when battery was not connected to PNP emmiters.

But i eliminated that version of circuit because problem of voltage gain and oscillations like you said but i must introduced some solution in this circuit to avoid high current flow when battery is not  connected onto collectors.

 

 

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So, this is circuit i want to make controled battery discharge with and as i said don't work as i expected.

When i connect power supply unlimitet current want to flow through circuit bit i don't know why?

 Maybe you are confused with my comment about power supply, no, i just use power supply from this forum to power this discharged circuit!

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Like I said, maybe an output transistor is shorted (or wired wrong) making the output voltage of the power supply as high as it can go. Since you removed the BD139 transistor then the diode D10 on the original schematic connected to it and to the project's output conducts and forces the output of the opamp to a high voltage and maybe destroying the opamp. 

I tried to replace OP and BD139 and there is the same story, when i connect base on BD139 then try to flow unlimitec current from power supply, i have not connected battery at all.

I also chech the output transistor and seems ok.

Its logical that current want to flow through output transistor because its forward orientated (base voltage higher than colector voltage) but i put 0V from negative feedback and there should no current flow at start???

 

 

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What do you mean with diode D10??

I have not diode in my circuit??

 

 

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Today i tried to measure some values, at first i was measuring voltages, when i remove BD139 out of circuit voltage on output pin of OP is 22,8V although the input voltage is 0V.

This is not OK?

If i put BD139 back in circuit and try connect it to my power supply unit (0-30V power supply from this website) off course i have short circuit, so unlimite current wanted to flow through BD139, so what do you think now what should goes wrong there??

 

 

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The opamp , BD139 or an output transistor is shorted.

I was also wondering this because before when I used PNP output transistor in common emmiter orientation if you remember circuit all works fine, the main probmel was as you said ringing because voltage gain.

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If you have 0V on the (+) input pin of the LM324 opamp and its (-) input is at a positive voltage of about 0.6V then its output should be as low as it can go which is about 0.01V so thall the transistors should be turned off.

 

If the voltage at the 0.5 ohm resistor is 0.6V then the bases of the output transistors should be about 0.86V and the base of the BD139 should be about 1.6V. Then the input should be 0.6V. When the input voltage is less then the voltage at the 0.5 ohm resistor should be the same.

Yes, but if I put 0V on + input pin of OP, on - pin should be 0V or not?

So on power resistor 0,5E should be 0V and no current should flow through battery, why in my case flow around 1A through BD139 when I connect power supply on circuit so 24V??

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This is circuit for my battery discharge but there is few problems which appear during test, at first when relay is off (two switches on battery) current flows via bd139 because the power transistors is forward biased there is maybe other solution for this for example another switch or SLT.

I don't know why OP folower doesn't work properly any more, if i put on OP + input pin zero voltage from MCU, is should be the same value on - input pin of OP but it isn't, there is always some value, in last case was 0,6V so 1,2A current was flow through BD139 and power transistors.

If you have any solution please let me know and one more time thanks for all your help!

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This thread has been for such a long time that most schematics are gone. I do not know what you want to do.

A charger puts current into a battery from a voltage higher than the battery voltage. The current is limited or regulated.

A battery is discharged by a load that draws current out of the battery. The load current is limited.

Yes, thanks for all your help, I just was afraid that discharging doesn't work in that kind of circuit orientation but such design work correctly for now, I mean you proposal NPN follower.

 

 

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No. An emitter resistor is not needed for only one output transistor.

Are you discharging a 12V battery? My circuit with an NPN driver transistor and NPN output transistor is a battery

charger

, not a discharger.

So, what is difference between charger and discharger, my idea was in switching relays which reconnect lines and provide both orientation??

What do you think about that?

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No. An emitter resistor is not needed for only one output transistor.
Are you discharging a 12V battery? My circuit with an NPN driver transistor and NPN output transistor is a battery charger, not a discharger.

sorry but I will very grateful if you give me advice about discharge circuit, I know that my version will wok but probably you have some critical comment, you have more experience!

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I want to use circuit above but instead of supply on power transistor there is battery which discharges, for charge it we use power supply voltage, so different orientation of circuit.
Is there any calculation for additional RC pole, in my current circuit remains some ripple with one single rc pole (470E + 1u capacitor).
I have to see in my program for frequency I forget it.

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No. An emitter resistor is not needed for only one output transistor.
Are you discharging a 12V battery? My circuit with an NPN driver transistor and NPN output transistor is a battery charger, not a discharger.

what is your suggestion?

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Instead of power supply we use battery for supply circuit and it stars discharged over load resistor and npn transistor.
Because of adjustable pwm voltage we regulate fixed discharged current, I think that this circuit is ok with npn follower circuit and transistors mentioned above.

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yes, I want use in both direction, one circuit is provide battery discharge for analyze it, other is for charge bit only optionally, the main purpose is only discharger, since is not big difference between circuit.

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If i use just one power transistor for max. 10A discharched current i should use emmiter resistor also for voltage drop on it, i think that 0.22 or 0.33E is ok.
What about noise from negative feedback of OP, i think that its better to use capacitor between negative pole of OP and ground?

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OP is LM324, i think that it should be ok

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TNX for suggestions, i use 24V Vcc supply voltage in my current version so i must calculate R2 for proper voltage drop on it, i think so.
Should i use MJ15003 NPN output power transistors in combination with some kind of BD139 transistor?
MJ15003 transistor has a small thermal resistance factor so it can decrease heat dissipation to heatsink.

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Is this ok?

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So, which circuit you finnaly suggest for me with two power transistor if it's need?

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Is this OK if we look back to my first version of circuit?
This is what I was thinking about and I think this is the most easy for correction my current version of circuit, I just want to add another transistor on my heat sink to decrease temperature on it.

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thanks for your help!
i will thinking about my circuit and which material i have available for this project and maybe i should corrent my current circuit

i have onother PNP transistor and how should i connect each other in parallel to decrease dissipation of single transistor and therefore obtain less temperature on my heatsink, i think that it's quite same than with npn which must have emmiter resistor to equalize current through both transistor, it isn't?