This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS61288: TPS61288

Part Number: TPS61288


I need your help desperately.

With E2E help, I built a prototype to test, see attached schematic. it consists of 2 portions: TPS61288 boost circuit and a Vin clamp/cut-off circuit (D1,Q1,Q2, D3).

Design goal: Battery voltage 8V~15V, boost output 12V 1.2A (max 1.4A).

The boost circuit alone works well. At Vin close to 12V, the ripple does very high(Vpp=1V). I add an 270uf aluminum cap, the ripple drops to 70mV. When Vin >12V, it directly goes to the Vout.

The Vin clamp/cut-off circuit alone works well too. When Vin <7.2V, Vin is cut off. When Vin in range 7.3V~12V, Q3 output 7.3V~12V. when Vin >12V, Q3 output 12V (when R6=11K).

However, when I connect Q3 output to boost input. It has an audible noise , and Vout is only 9V.

  1. I change L1 to 10uH, doesn’t help.
  2. I change zero/pole distribution by change C7 to 30pf, doesn’t help.
  3. I add a 100uf aluminum cap at Q3 output , doesn’t help.

I am really frustrated, seek help from you.

Thanks.TPS61288 schematic.pdf

Chang Cao

  • I think Q3 is not compatible with boost circuit. I disconnect Q2 emitter from Vin line; disconnect Q3 base from the joint of D2 cathode/R5/R6; connect a 1K resistor to Q3 base, so now only Q3 is connected to the boost circuit (1K provides base current). Still have audible noise. very wierd,  (Vin=9V, boost input 6.85V, boost vout=6.52V, voltage not step up.

    Q3 not saturated. for 12V boost output, if boost vin is only 6V, the input current should be twice of the output current which ~2.4A(i use1.2A load). Q3 is ZXT1053AK , whose hfe(min)=300(Ic=1A); hfe(min)=50(Ic=5A); it seems 1K base resistor is ok

  • Hi Chang Cao,

    Your analysis is right, Q3 might be not saturated.

    It is likely that the sink current is not as large as you calculated.

    You can try to add a voltage source 15V directly series in 1K to base of Q3, this can ensure the saturation and you can see if the system is stable.

    then you can have a test of the base current and to see why it was inadequate.

    Best Regards