Hello World,

Im reading the book "the art of electronics - horowitz hill", There is a part of the book wich it has "bad circuits", i would like to know whats the problem in that circuits(check pictures),
Whats wrong and why in each circuit?
Thank you all!!!!


[pic 1]


[pic 2]


[pic 3]

 

PIC1 - No current limiting on that base, Zener will cook (assuming that it works)
PIC2 - No current limiting on the input and there is a cross over issue
PIC3 - I think there is no feedback so as the loads resistance changes the current through the load will also change (but thats assuming its a constant current source)

 

pic1 , no current limiting resistor.

Pic2 - the position of the NPN and pnp should be switched (you will have a short circuit at 0v (look up "shoot through" ))

Pic3 - the pnp is upside down (emitter should be pointing in direction of current flow). Also, if you want to switch on the low side of the load, use an NPN.

 

PIC1 - No current limiting on that base, Zener will cook (assuming that it works)
PIC2 - No current limiting on the input and there is a cross over issue
PIC3 - I think there is no feedback so as the loads resistance changes the current through the load will also change (but thats assuming its a constant current source)

Pic1 is correct, pic2 and pic3 need to be fixed.

 

@GopherT misread that PNP as an NPN

 

@GopherT misread that PNP as an NPN

Which one?

 

PIC3. Even then, its a terrible circuit

 

But guys, how to solve it in each circuit?

 

PIC3. Even then, its a terrible circuit

Pic3 is a PNP - notice the arrow pointing in.

 

But guys, how to solve it in each circuit?

The solution is to identify the error.

 

Yup, I misread it as a NPN!

 

@OBW0549 what do you think about that circuits?

 

See ee

 

@OBW0549 what do you think about that circuits?

The first circuit is missing a resistor between Vin and the Zener diode to give the diode proper operating current. The voltage across the diode will be zero, as will the circuit output voltage.

In the second circuit, there is a direct, unlimited current path from +Vcc to -Vee. Current flows into the emitter of the top transistor, through the B-E junction, down to the base of the bottom transistor, through its B-E junction and into -Vee. Both transistors catch fire, along with the power supply.

The circuit in pic3 uses the wrong kind of transistor. The transistor should be an NPN, not a PNP.

 

The first circuit is missing a resistor between Vin and the Zener diode to give the diode proper operating current. The voltage across the diode will be zero, as will the circuit output voltage.

In the second circuit, there is a direct, unlimited current path from +Vcc to -Vee. Current flows into the emitter of the top transistor, through the B-E junction, down to the base of the bottom transistor, through its B-E junction and into -Vee. Both transistors catch fire, along with the power supply.

The circuit in pic3 uses the wrong kind of transistor. The transistor should be an NPN, not a PNP.

So, in second picture, what could we do for solve it? I mean, maybe changing kind of transistor? or maybe we cant do anything to solve it...
Thank you very much!

 

So, in second picture, what could we do for solve it? I mean, maybe changing kind of transistor? or maybe we cant do anything to solve it...

It looks to me like the circuit is intended to portray a basic push-pull emitter follower circuit, but with a mistake. If so, the way to fix it is to exchange the positions of the two transistors, keeping their orientations the same. In other words, the collector of the NPN goes to +Vcc, the collector of the PNP goes to -Vee, the two bases are connected together as the input, and the two emitters are connected together as the output.

 

It looks to me like the circuit is intended to portray a basic push-pull emitter follower circuit, but with a mistake. If so, the way to fix it is to exchange the positions of the two transistors, keeping their orientations the same. In other words, the collector of the NPN goes to +Vcc, the collector of the PNP goes to -Vee, the two bases are connected together as the input, and the two emitters are connected together as the output.

Thank you very much! I got it

 

It looks to me like the circuit is intended to portray a basic push-pull emitter follower circuit, but with a mistake. If so, the way to fix it is to exchange the positions of the two transistors, keeping their orientations the same. In other words, the collector of the NPN goes to +Vcc, the collector of the PNP goes to -Vee, the two bases are connected together as the input, and the two emitters are connected together as the output.

Man, you need to teach me how to make those confidence-building hand gestures as I answer the questions.

 

Man, you need to teach me how to make those confidence-building hand gestures as I answer the questions.

@GopherT Dont think bad on me please, your answers were correct too. Just I only wanted to know how to fix it, thats why I asked.
I was some confused.
But I thank you very much for your time and your answers, and believe me I have them in mind,

Regards

 

@GopherT , @Robin Mitchell , @OBW0549 I also saw others circuits in the same book(pic7-9), which have problems too. What do you think about it?
Thank you very much to all!