Help to understand the operating logic of the Bosch charger

Thread Starter

maher4712

Joined Sep 2, 2020
7
hi,
I ask for your help to:
  1. determine, if possible, the type of transistor T5, T7 (SMD code: MK3C).
  2. help me to understand the operating role of the set T5, T7 and R23, R33 in the circuit (it's like a logical port type AND, but I do not understand how it works).
  3. help me understand why the feedback control of the battery voltage made by R38 + R43 before the diode SK34F and not after.
To simplify the repair I made a schematic by reverse engineering; diagram and other photos are below.
 

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ronsimpson

Joined Oct 7, 2019
1,996
T5,7 are transistors.
The "23V" flows along the orange wire through T5, T7, Diode to battery. T7 is controlled by T6 which is controlled by the IC. For the battery to charge both T5 and T7 must be turned on. When the IC thinks the battery is charged or is too hot T7 turns off while T5 is on. Now only a small trickle of current charges the battery. If the voltage gets too high (over charge) T5 can be turned off to completely stop charging.
 

Thread Starter

maher4712

Joined Sep 2, 2020
7
T5,7 are transistors.
The "23V" flows along the orange wire through T5, T7, Diode to battery. T7 is controlled by T6 which is controlled by the IC. For the battery to charge both T5 and T7 must be turned on. When the IC thinks the battery is charged or is too hot T7 turns off while T5 is on. Now only a small trickle of current charges the battery. If the voltage gets too high (over charge) T5 can be turned off to completely stop charging.
 

Thread Starter

maher4712

Joined Sep 2, 2020
7
T5,7 are transistors.
The "23V" flows along the orange wire through T5, T7, Diode to battery. T7 is controlled by T6 which is controlled by the IC. For the battery to charge both T5 and T7 must be turned on. When the IC thinks the battery is charged or is too hot T7 turns off while T5 is on. Now only a small trickle of current charges the battery. If the voltage gets too high (over charge) T5 can be turned off to completely stop charging.
thank you for your reply, if i understand the small trickle of current charges the battery through R33, can you tell me the role of r23, and if possible the answer for question 3
 

ronsimpson

Joined Oct 7, 2019
1,996
I agree that it would be more accurate to measure voltage at the battery not (battery voltage + 1Diode). If the voltage divider was directly on the battery, it will discharge the battery after a month.

R23: When T5 is open it pulls that pint to ground. Big Schottky diodes are leaky, some current will flow back through the diode. With out R23 the IC will measure some strange unpredictable voltage when T5 is open.
 

Thread Starter

maher4712

Joined Sep 2, 2020
7
Je suis d'accord qu'il serait plus précis de mesurer la tension au niveau de la batterie non (tension de la batterie + 1 Diode). Si le diviseur de tension était directement sur la batterie, il déchargera la batterie au bout d'un mois.

R23 : Lorsque T5 est ouvert, il tire cette pinte vers la terre. Les diodes Big Schottky fuient, du courant reviendra à travers la diode. Sans R23, le circuit intégré mesurera une tension étrange et imprévisible lorsque T5 est ouvert.
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merci beaucoup c'est clair pour moi maintenant
 

Thread Starter

maher4712

Joined Sep 2, 2020
7
i have try some combination : dual NPN : not work / dual PNP : work well / dual N-Mosfet : Not work / dual P-Mosfet : not tested (I do not have) but i think it will be work,
for the replacement of the MK3C what you suggest to me, uses two PNP or P-Mosfet
 

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