# Help joule thief circuit

#### lawnd

Joined May 10, 2018
1
i was completed my small project with simple joule thief circuit, and I made inductor with L1 = 10L L and L2 = 110 L with same in string diameter. Input is 1,5 V with the output is -16 V.
and my question,
-Why the output is -16V?
-What components should be added so that the output is not negative and stable?

#### rutendo

Joined Sep 24, 2017
10
L see you are using an npn transistor and if you look over the voltage signal in an oscilliscope you will see the waveform is basically oscillating and an npn inverts the signal and hence negative.L hope ; answered your question

#### DickCappels

Joined Aug 21, 2008
7,147
How are you measuring the output? (Average, peak, RMS?)

Without a rectifier the average output voltage should be very close to 1.5V.

#### wayneh

Joined Sep 9, 2010
17,018
I believe the windings in your secondary are the reverse polarity of what you want. Can you turn the connections around?

#### DickCappels

Joined Aug 21, 2008
7,147
I believe the windings in your secondary are the reverse polarity of what you want. Can you turn the connections around?
When the collector is low the base is driven more positive until something runs out (core saturates, the base drive becomes inadequate, etc.). That is the way this oscillator works.

#### wayneh

Joined Sep 9, 2010
17,018
When the collector is low the base is driven more positive until something runs out (core saturates, the base drive becomes inadequate, etc.). That is the way this oscillator works.
So you get a negative voltage by design? Clever.

#### DickCappels

Joined Aug 21, 2008
7,147
When the transistor eventually switches off you can get a pretty large positive flyback pulse. I don't see how it could go negative, that is why the question about the measurement method.

Somebody once wrote to me saying that he used a germanium transistor in this circuit to light a neon bulb when operating from a single silicon solar cell, putting out just over 0.6V. Amazing.

#### wayneh

Joined Sep 9, 2010
17,018
When the transistor eventually switches off you can get a pretty large positive flyback pulse. I don't see how it could go negative...
Well what I was suggesting was that the secondary of the coil was oriented opposite as shown in the diagram. Murphy's Law. But I suppose it wouldn't oscillate that way. Which leaves the simpler hypothesis that the meter's leads were reversed.

#### DickCappels

Joined Aug 21, 2008
7,147
I like both. Right, some people making these things do not get the phasing dots right.

Let's see what the TS reports

#### Colin55

Joined Aug 27, 2015
519
How many wrong and misleading answers can you get in one discussion?